This invention relates in general to a Thermite welding process and a multi-function digital pressure measuring device used with a welding torch during the process. More specifically, the invention relates to the regulation and display of the gas pressures to the torch head and tracking the amount of time required for the preheat process during Thermite welding. Numerous applications exist in the welding field wherein the user desires to monitor the gas pressure at the torch rather than just at the pressure regulator located back at the tank. One reason is due to the substantial pressure drop that occurs when using a long hose between the tank and the torch head as seen in many railroad rail welding applications.
Thermite welding is utilized to join railroad tracks together into a single length of track The objective of Thermite welding of rails is to properly and permanently join two pieces of rail, end to end, with a butt weld. This is done by casting molten steel into refractory molds that have been placed around the spacing between the two rails.
During this process the rails must be preheated to a minimum of 1100 to 1800 degrees Fahrenheit. To obtain the proper preheat, welders us a mixture of oxygen and propane. A line pressure of 65 psi is required for oxygen while the propane line pressure is maintained at 15 psi. It is critical to maintain the proper pressures during preheat of the Thermite weld in order to obtain the proper weld. Since the temperature of the weld is not directly measured it is calculated to be in the range necessary to provide a good weld by a welder knowing both the pressure of the oxygen and propane at the torch head and the length of time of the preheat. If the preheat temperature isn't sufficient, the weld will be flawed and will be required to be redone. Preheating is a timed consideration based on maintaining the gas pressures as specified. Generally, the preheating required is a minimum of 5 minutes. One of the problems is that currently the welders use small inaccurate analog gauges to assure line pressure. These gauge are often damaged as the welding gas hoses are dragged from place to place and even in some cases driven over by vehicles. It has been determined that the best way to ascertain that the appropriate temperature has been obtained is by timing the preheat process at the proper gas pressures. Generally, a welder uses a stop watch to keep track of the preheat time. However, the stopwatch is often lost, broken, or just forgotten. The welder then uses a wrist watch or merely guesses as to the time elapsed during the preheat. Either method is unacceptable. If the welder has guessed at the time and waits longer than necessary, unnecessary amounts of oxygen and propane are expended which drive up the cost of the weld. If the welder guessed at a time too short then a flawed weld will occur, which again drives up the cost of the weld as it has to be redone.
Another problem with the currently used analog gauges is that they are not easily observed during the welding process and are inherently inaccurate. In an attempt to overcome this problem, larger and more accurate analog gauges were used. However, due to their size and weight they are also often broken.
Additionally, another problem in the field of welding is the hazard presented by a ‘flashback’. Flashback can occur if the torch is not properly turned off. The flame travels up the hose connecting the torch to the tank of gas and ignites the entire tank Obviously, such events are extremely dangerous. To prevent flashbacks, a device known as a “Flashback Arrestor” is installed on the hose at the welding torch. These devices are common in the industry and available from numerous welding supply manufacturers. However, they have a limited life and should be replaced on a regular basis. For example, several railroads require that the Flashback Arrestor be replaced every year. It is difficult to track the length of time the Flashback Arrestor has been in use and insure that it is replaced before it becomes ineffective. A multi-functional digital pressure measuring 6(b) is attached to flashback arrester 53 so that it is replaced before it becomes ineffective.
U.S. Pat. No. 5,278,388 to Huang teaches the use of a discharge passage when pressure exceeds a predetermined pressure to maintain constant pressure at a welding head. However, it doesn't eliminate the problem with the low pressure. U.S. Pat. No. 5,317,126 to Courch, Jr., et al. uses an experimental pressure gauge to check the nozzle pressure, but such would be impractical and cumbersome.
There are numerous devices that have inline pressure gauges. However, these are the same type of gauges currently being used. Examples are shown in U.S. Pat. No. 6,029,361 to Newman, U.S. Pat. No. 5,062,898 to McDermott et al., U.S. Pat. No. 4,884,410 to Bell et al, and U.S. Pat. No. 5,440,918 to Oster.
U.S. Pat. No. 6,210,492 to Wilson III shows an inline analog pressure gauge which is similar to that currently in use in the Thermite welding process.
U.S. Publish Patent Application No. 2003/0025000 to Schmon et al., shows digital read out of pressure in the handle of the paint spray gun which is not easily readable during usage. One must stop spraying to check the air pressure which in and of itself is not desirable in the current application as it is necessary to know both that the time and that the pressure has been maintained during the preheat process.